Barometric pressure (BP) in an engine intake of a vehicle may vary due to altitude changes of the vehicle. Thus, an accurate assessment of barometric pressure changes experienced by an engine of a vehicle may be beneficial for improved operation of the vehicle. In particular, diagnostic functions, e.g., leak diagnostics in an evaporative emission control system, and engine strategies, e.g., air/fuel ratio estimates and spark timing, may benefit from having an accurate estimate of barometric pressure. For example, an evaporative leak check monitor may false fail or false pass if the BP is changing due to altitude changes or weather phenomenon. As another example, evaporative leak check detection thresholds may be adjusted in response to changes in altitude. BP determination in an engine typically relies on a barometric pressure sensor in an intake of the engine, e.g., a manifold air pressure (MAP) sensor in the engine intake.
The inventors herein have recognized various issues with approaches which rely on a MAP sensor for accurate BP determination. In particular, approaches which utilize a MAP sensor for determining barometric pressure rely on part throttle or full or wide open throttle conditions, e.g., cruising or going up a hill, in order accurately determine BP. However, during closed throttle conditions, e.g., during downhill driving, or if a fault is present in a MAP sensor, the MAP sensor may not be able to be used to infer BP. During these conditions, engine operation and diagnostic routines may become degraded since an accurate determination of BP is not possible. For example, lack of altitude detection can result in alpha/beta errors in an evaporative diagnostic monitor (ideally, the monitor should abort execution if a significant altitude change is detected). In some approaches a global positioning system (GPS) may be included in a vehicle to determine altitude changes. However, not all vehicles have GPS technology and there may be remote geographical areas where GPS reception is not available. Thus GPS technology for altitude determination may be unreliable or costly.
In one example approach, in order to at least partially address these issues, a method for detecting barometric pressure changes in a vehicle with an engine comprises adjusting an evaporative leak detection threshold based on a change in barometric pressure, where the change in barometric pressure is based on a tire pressure change. For example, a tire pressure change may be determined via one or more tire pressure sensors and used to indicating an altitude change based on the tire pressure change. Various engine operating conditions and diagnostic routines may then be adjusted based on the BP change detected via the tire pressure change. For example, an evaporative leak detection monitor may be discontinued in response to a change in altitude determined from the tire pressure change. As another example, an engine air/fuel ratio may be adjusted in response to a change in altitude determined from the tire pressure change.
In this way, tire pressure sensors coupled to one or more tires of a vehicle may be utilized to determine changes in barometric pressure during fault conditions of a MAP sensor, e.g., during closed throttle conditions. Since such tire pressure sensors are ubiquitous, such an approach provides a consistent and accurate approach to BP determination so that vehicle operation may be optimally adjusted during all conditions. Utilizing readily available tire pressure sensors, altitude changes can be detected and used to increase robustness of diagnostic routines and engine air/fuel control.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above of in any part of this disclosure.